The conventional ion concentration sensors (for example, ion sensitive FETs (ISFET: Ion Sensitive Field Effect Transistor) for detecting a hydrogen ion concentration) have problems of low sensitivity, temporally varied outputs, and the like. As a solution for such problems, a structure has been suggested which detects an amount of a change in electric potential level of a channel which change is based on a change in electric potential level of a surface of a sensing section. The structure requires elements such as an input transistor, an output transistor, and a reset transistor. Therefore, it is difficult to form a fine cell having a size of not more than 10 μm.
The structure has those transistors in each cell. Therefore, not only the sensing section but also a variation in characteristic between such elements in the each cell acutely affects accuracy of readout electric charge. This ultimately causes a great variation in accuracy of the readout electric charge between cells, thereby bringing a problem such that the accuracy is not improved. In view of this, in order to fix a measured value, it is necessary to (i) measure the characteristic of each cell in advance, (ii) create a standard curve in accordance with a result of such measurement, (iii) store data on the standard curve, and (iv) check measurement data with such stored data. This takes a lot of time and labor.
For example, a sensor disclosed in Patent Literature 1 includes an input diode which supplies electric charge, an output gate, and a reset diode. Meanwhile, a sensor disclosed in Patent Literature 2 includes an input diode, an output gate, and a reset section. A sensor disclosed in Patent Literature 3 includes an input diode, an output transistor, and a reset diode. Each of the sensors disclosed in Patent Literatures 1 through 3 is thus arranged such that such elements are provided with respect to one sensing section. Therefore, each of the sensors disclosed in Patent Literatures 1 through 3 has a problem as described above.
In order to solve such problem, Patent Literature 4 discloses a structure similar to an interline CCD (Charge Coupled Device), which is configured such that an electric charge transfer section transfers capacitive electric charge and a section in a vicinity of a sensor converts the capacitive electric charge to a voltage. According to the structure, it is not necessary to provide a reset transistor and an output transistor in each cell. However, the structure still needs an electric charge injection section such as an electrode and a non-sensitive membrane.